This invention relates to the sector of rotary positive-displacement pumps. Various types of rotary pumps are known, amongst which are gear pumps, lobe pumps and screw pumps.
Gear pumps generally consist of two gear wheels, one of which, termed the driving gear, is connected to a drive shaft and drives the other gear, termed the driven gear, in rotation.
Document EP-1 132 618 by the same applicant, relates to a rotary positive-displacement gear pump in which the gear wheels comprise a plurality of meshing teeth without encapsulation and at the same time incorporating helical teeth with face contact substantially equal or close to unity. The combination of a tooth profile which avoids encapsulation and the helical development of the teeth reduces the ripple and noise resulting from it while the pump is operating.
Experiments carried out by the applicant on various gears to be used in pumps of known type of the type indicated above revealed that there is a defined range of tooth profiles which can be effective both in reducing the noise of the pump and at the same time in making manufacture relatively simple, which may assist in containing the production costs of positive-displacement pumps. Moreover, this series of specifically identified profiles has the advantage of a high level of reliability in use, which makes its use in positive-displacement pumps for high pressures particularly advantageous.
In order to achieve the aims indicated above, the subject of the invention is a gear wheel with a plurality of teeth capable of meshing with the teeth of another corresponding gear wheel, the profile of each tooth of the gear wheel, in cross-section, being defined in the claims below.
In particular, the profile of at least one tooth of one of the two rotors is defined by a natural spline function passing through a plurality of nodal points having pre-established coordinates, with a tolerance of xc2x1{fraction (1/20)}th of the depth of the tooth on the theoretical profile defined by the plurality of preferred nodal points. The nodal points are defined by a pair of values {Xxe2x80x2, Yxe2x80x2} expressed in a system of Cartesian coordinates having their origin at the centre of the pitch circle of the gear wheel.
A further subject of this invention is a rotary positive-displacement pump comprising a pair of meshing gear wheels having a tooth profile of the type indicated above.